Ion release, biocompatibility, and bioactivity of resin-modified calcium hydroxide cavity liners.

BACKGROUND: The placement of liners near the pulp area is essential for therapeutic effects and maintaining pulp health while stimulating the formation of tertiary dentin. This in vitro study aimed to evaluate the calcium release, pH, biocompatibility, solubility, and bioactivity of three resin-modified calcium hydroxide cavity liners. METHODS: The disc specimens of each cavity liner were prepared using polyethylene molds of 7 mm in diameter and 2 mm in height (n = 10). Three light-cure liners evaluated include Ultra-Blend Plus (UB), Base-it (BI), and Master Dent (MD). The samples were then immersed in flasks containing 10 mL of distilled water. Calcium ion release, pH, and solubility were evaluated in two weeks of incubation. The cytotoxicity of extracts adjacent to the specimens was evaluated by MTT assay using NIH/3T3 cells after 1, 3, and 7 days of incubation. The ability to induce the nucleation of calcium phosphates (CaPs) after 28-day immersion in a simulated body fluid was investigated by SEM-EDX analysis. Statistical analysis was performed using ANOVA, Kruskal-Wallis, and repeated measures tests at the significant level of 0.05. RESULTS: There was a significant difference in the release of calcium ions among the three liners investigated on days 1, 7, and 14 (p < 0.05). UB liners exhibited a significantly higher amount of calcium release than the other two liners, followed by BI, and MD. On day 1, there was no significant difference in the average pH among the three liners. However, after day 7, the MD liner showed a significant decrease in pH compared to the other two liners. BI liner demonstrated the highest level of biocompatibility, followed by the MD and UB liners. UB showed a high calcium release, solubility with no alkalizing activity, and the formation of more mature Ca-rich apatite deposits than the other two liners. CONCLUSION: Based on the results of this study, the cavity liner material's performance is material dependent. It can impact ion release, biocompatibility, and bioactivity which are important factors to consider in clinical practice. Further studies are needed to investigate the long-term effects of different liner materials on oral tissues.

Comparative Effect of two Types of Surface Treatments on Shear Bond Strength of New Composite to Old Composite.

STATEMENT OF THE PROBLEM: Composite restoration failures may occur because of different factors. In these situations, the repair of a composite restoration has many advantages over replacement such as saving time, lower cost, and lower risk of excessive removal of sound tooth structure and subsequent pulp exposure. PURPOSE: The purpose of this in vitro study was to evaluate the effects of two surface treatments on shear bond strength (SBS) of new composite to old composite. MATERIALS AND METHOD: In this in vitro study, 60 composite discs were fabricated using a plexiglass mold measuring 4 mm in thickness and 7 mm in diameter, and were randomly divided into three groups (n=20). In group 1, the bonding procedure was done with no modification. After roughening of one surface in all remaining samples, chloroform (CHCl3) was applied on the surface of samples in group 2 and phosphoric acid 35% was applied on the surface of the samples in group 3. PermaSeal was then applied in all samples and new composites were bonded to the surface. The samples were stored in distilled water for one week and were then subjected to 500 thermal cycles and shear bond strength between two layers of composite and mode of failures were evaluated. RESULTS: The lowest and the highest SBS values of repair composite to old composite were noted in groups 3 and 1, respectively and this difference was statistically significant (p< 0.05).The difference between groups 1 and 2 was not significantly different (p= 0.197). The mode of failure was mixed in all samples of groups 2 and 3 and cohesive in group 1. CONCLUSION: After grinding, the surface treatment with phosphoric acid did not increase the SBS of new composite to old composite, while chloroform increased the SBS almost to the level of the baseline in control group.

Micro-computed tomography in preventive and restorative dental research: A review.

PURPOSE: The use of micro-computed tomography (micro-CT) scans in biomedical and dental research is growing rapidly. This study aimed to explore the scientific literature on approaches and applications of micro-CT in restorative dentistry. MATERIALS AND METHODS: An electronic search of publications from January 2009 to March 2021 was conducted using ScienceDirect, PubMed, and Google Scholar. The search included only English-language articles. Therefore, only studies that addressed recent advances and the potential uses of micro-CT in restorative and preventive dentistry were selected. RESULTS: Micro-CT is a tool that enables 3-dimensional imaging on a small scale with very high resolution. In this method, there is no need for sample preparation or slicing. Therefore, it is possible to examine the internal structure of tissue and the internal adaptation of materials to surfaces without destroying them. Due to these advantages, micro-CT has been recommended as a standard imaging tool in dental research for many applications such as tissue engineering, endodontics, restorative dentistry, and research on the mineral density of hard tissues and bone growth. However, the high costs of micro-CT, the time necessary for scanning and reconstruction, computer expertise requirements, and the enormous volume of information are drawbacks. CONCLUSION: The potential of micro-CT as an emerging, accurate, non-destructive approach is clear, and the valuable research findings reported in the literature provide an impetus for researchers to perform future studies focusing on employing this method in dental research.

The effect of composite resin preheating on marginal adaptation of class II restorations.

BACKGROUND: One of the problems with a high filler content composite resins is gap formation at restorative material-tooth interface. The present study investigated the effect of preheating composite resins on the formation of marginal gap in Cl II restorations. MATERIAL AND METHODS: In this in vitro study Sixty Cl II cavities were prepared on the mesial and distal surfaces of 30 extracted premolar teeth. The gingival floor of cavities was placed 1 m below the CEJ. The samples were randomly allocated to 4 groups for restoration placement: group 1, Filtek P60 composite resin at room temperature; group 2, Filtek P60 composite resin at 68°C; group 3, X-tra fil composite resin at room temperature; and group 4, X-tra fil composite resin at 68°C. After a thermocycling procedure, the teeth were sectioned longitudinally in a buccolingual direction. Then the marginal gaps of the samples were measured at proximal and gingival margins under a scanning electron microscope at ×2000 magnification in µm. The data were analyzed with SPSS 21, using one-way ANOVA, post hoc Tukey tests and paired t-test (α=0.05). RESULTS: Groups 2 and 4 exhibited significantly lower marginal gaps, compared to groups 1 and 3, at both enamel (P<0.0001 and P=0.001, respectively) and dentinal walls (P<0.0001). In all the groups, there was significantly less marginal gaps at composite-enamel wall compared to composite-dentin wall interfaces (P<0.0001). There was no significant difference between groups 1 and 3 and groups 2 and 4 in enamel walls (p= 0.96, p= 0.99 respectively) and dentinal walls (p= 0.85, p=0.98 respectively). CONCLUSIONS: Preheating resulted in a decrease in marginal gaps in both composite resins. The effect of composite resin type on marginal adaptation was the same. Key words:Composite resin, dental marginal adaptation, preheating.

In Vitro Comparative Evaluation of Newly Produced Desensitizer, Chlorhexidine and Gluma on Bond Strength and Bond Longevity of Composite to Dentin.

STATEMENT OF THE PROBLEM:  Etching process on dentin can activate matrix metalloproteinase (MMP) which hydrolyze organic matrix of demineralized dentin. Gluma and chlorhexidine could inhibit the activation of MMP. PURPOSE:  The aim of the study was to evaluate the effect of a new desensitizing material consisting of Gluma and chlorhexidine together on the shear bond strength and bond durability of composite restorations. MATERIALS AND METHOD: One hundred and twenty caries-free extracted premolars were sectioned horizontally from one third of the coronal crown to expose flat dentin surface and randomly divided into 4 groups. In the control group, no surface treatment was used. In the first group chlorhexidine (CHX) 2%, in the second group, new material (NM) and in third group Gluma desensitizer (GD) was applied after etching and before bonding(total-etch bonding system). After the bonding process, the composite was placed on the surface of the samples using a cylindrical mold. Then, the shear bond strengths of half of the specimens were measured after 24 hours and the other half after 6 months of storage in distilled water and thermocycling. The failure types of specimens were evaluated with a stereomicroscope. Data were analyzed using One-way Anova and Tukey's Post Hoc tests in SPSS software. RESULTS:   After 6 months, the bond strength decreased in all groups and differences were statistically significant (p= 0.002).The highest shear bond strength was observed after 6 months in the NM group and the GD group with no statistically significant difference. The 24-hour bond strengths were not significant between groups. Mix failure had the highest rate in all groups. CONCLUSION:  It can be concluded that the effect of combination of chlorhexidine and Gluma on maintaining the integrity and strength of bond over time is similar to Gluma compound alone and they have better effect than chlorhexidine.

A Comparative Evaluation of Microleakage of Two Low-Shrinkage Composites with a Conventional Resin Composite: an In Vitro Assessment.

STATEMENT OF THE PROBLEM: Polymerization shrinkage stress in composite restorations may lead to microleakage. Clinical methods such as using low-shrinkage composites have been suggested to overcome this problem; however, there are controversies about their efficiency in decreasing the microleakage. PURPOSE: This in vitro study was conducted to compare the microleakage of two low-shrinkage resin composites with a conventional one. MATERIALS AND METHOD: Fifty class V cavities of 2.5×3×2 mm (depth× length× width) were prepared in the buccal surfaces of intact bovine incisor teeth with the incisal margin on the enamel and gingival margin on the cementum. The teeth were randomly divided into 5 groups. In group 1, Clearfil APX (conventional) with SE Bond was used in 2 layers (Kuraray; Japan). In group 2, GC Kalore (low -shrinkage) with GC UniFil Bond was applied in one layer (GC Company). In group 3, the material of group 2 was applied in two layers. In group 4, FiltekP90 (low -shrinkage) with P90 System adhesive was applied in one layer (3M ESPE). In group 5, the materials of group 4 were applied in two layers. The samples were thermocycled and immersed in 0.5% fuchsin solution for 24h. The restorations were sectioned in buccolingual direction. Then they were evaluated for microleakage by using a stereomicroscope and scored as 0, 1, 2, and 3 and then Kruskal-Wallis test was used (p< 0.05). RESULTS: The groups were not significantly different regarding the microleakage in the coronal and cervical margins (p< 0.423 and p< 0.212, respectively); however, the Filtek P90 yielded the best results. In all groups, except group 5 (p= 0.018), the cervical margins had greater microleakage than the coronal margins. CONCLUSION: The results suggested that low-shrinkage resin composites may not reduce the marginal microleakage. The proper use of conventional resin composites may offer comparable clinical results.

The effects of noise reduction, sharpening, enhancement, and image magnification on diagnostic accuracy of a photostimulable phosphor system in the detection of non-cavitated approximal dental caries.

PURPOSE: Contrast, sharpness, enhancement, and density can be changed in digital systems. The important question is to what extent the changes in these variables affect the accuracy of caries detection. MATERIALS AND METHODS: Forty eight extracted human posterior teeth with healthy or proximal caries surfaces were imaged using a photostimulable phosphor (PSP) sensor. All original images were processed using a six-step method: (1) applying "Sharpening 2" and "Noise Reduction" processing options to the original images; (2) applying the "Magnification 1:3" option to the image obtained in the first step; (3) enhancing the original images by using the "Diagonal/" option; (4) reviewing the changes brought about by the third step of image processing and then, applying "Magnification 1:3"; (5) applying "Sharpening UM" to the original images; and (6) analyzing the changes brought about by the fifth step of image processing, and finally, applying "Magnification 1:3." Three observers evaluated the images. The tooth sections were evaluated histologically as the gold standard. The diagnostic accuracy of the observers was compared using a chi-squared test. RESULTS: The accuracy levels irrespective of the image processing method ranged from weak (18.8%) to intermediate (54.2%), but the highest accuracy was achieved at the sixth image processing step. The overall diagnostic accuracy level showed a statistically significant difference (p=0.0001). CONCLUSION: This study shows that the application of "Sharpening UM" along with the "Magnification 1:3" processing option improved the diagnostic accuracy and the observer agreement more effectively than the other processing procedures.

Effect of different decontamination procedures from a saliva-contaminated cured bonding system (Single Bond).

BACKGROUND: A few studies have investigated the effect of saliva contamination of cured or uncured adhesive systems. The aim of this study was to compare the effect of different decontamination methods on the shear bond strength of composite to enamel and dentin using an adhesive contaminated after light activation. MATERIALS AND METHODS: In this in vitro experimental study, 80 extracted sound human teeth, 40 premolars and 40 central incisors were selected for dentin and enamel specimen preparation. Within each of the two test groups, the teeth were randomly subdivided into five groups. The materials used consisted of single bond (3M) and Z250 (3M). Except group 1 (Control), in Groups 2-5, cured adhesive was contaminated with saliva (20 s). Decontaminating procedures were rinsing, blot-drying, rebonding (Group 2), rinsing, air-drying, rebonding (Group 3), etching, rinsing, blot-drying, rebonding (Group 4) and etching, rinsing, blot-drying (Group 5). Then, composite resin was inserted on the treated surfaces and cured. The results were subjected to one-way ANOVA and Tukey honestly significant difference (HSD) tests. RESULTS: Group 5 (etching, rinsing, blot drying) resulted in significantly lower bond strength to both enamel and dentin surfaces in comparison with the other groups (P < 0.05). CONCLUSION: When the adhesive was re-applied, all decontamination methods in this study seemed sufficient to decrease the adverse effect of saliva.